1. Field of the Invention
The present invention relates to spherical silica-titania-based fine particles that have been surface-treated with silane, and more particularly to spherical silica-titania-based fine particles surface-treated with silane which display superior dispersibility and low levels of aggregation. In addition, the present invention also relates to an external additive for a fine particle toner used for improving image quality.
2. Description of the Prior Art
Dry developers used in electrophotographic techniques and the like can be broadly classified into one-component developers that use solely a toner comprising a colorant dispersed within a binder resin, and two-component developers comprising a carrier mixed with the toner. When a copy operation is conducted using one of these developers, in order to achieve the required level of process compatibility the developer must display excellent levels of flowability, caking resistance, fixation, electrostatic chargeability, and cleanability. Inorganic fine particles are frequently added to the toner to improve the levels of flowability, caking resistance, fixation, and cleanability. However, the dispersibility of the inorganic particles has a large effect on the characteristics of the toner, and if the dispersibility is non-uniform, then the desired levels of flowability, caking resistance and fixation may not be achievable, and the level of cleanability may also deteriorate, causing toner adhesion to the photoreceptor and the appearance of black spot image defects. In order to resolve these types of problems, a variety of products have been proposed in which the surface of the inorganic fine particles has been subjected to hydrophobic treatment (see patent reference 1, patent reference 2, patent reference 3).
However, in those cases where either organic photoreceptors or finer particle toners are used to further improve image quality, the types of inorganic fine particles described above do not produce satisfactory levels of performance. The surface of organic photoreceptors is softer than that of inorganic photoreceptors and the reactivity is also higher, meaning organic photoreceptors are prone to reduced lifespans. Accordingly, when this type of organic photoreceptor is used, the inorganic fine particles added to the toner can cause degeneration or scratching of the photoreceptor. Furthermore when fine particle toners are used, because the powder flowability is poorer than that displayed by toners of a more conventional particle size, larger quantities of inorganic fine particles must be added, and these inorganic particles increase the likelihood of toner adhesion to the photoreceptor.
Accordingly, a process has been proposed which uses a specific silane treatment process for performing a hydrophobization of hydrophilic spherical silica fine particles produced by hydrolysis of an alkoxysilane (see patent reference 4). However, the level of electrostatic charging of the silica fine particles produced by this process is low, and even if used as a toner external additive, the particles are unable to impart the required level of electrostatic charge to the toner.
Furthermore, spherical silica-titania fine particles produced by the hydrolysis of metal alkoxides have been reported as composite inorganic oxides (see patent reference 5). However, these spherical silica-titania fine particles have a hydrophilic surface and consequently display inadequate dispersibility, and also display a large variation in the level of electrostatic charging depending on the environment.
[Patent Reference 1]
Japanese Laid-open publication (kokai) No. Sho 46-5782
[Patent Reference 2]
Japanese Laid-open publication (kokai) No. Sho 48-47345
[Patent Reference 3]
Japanese Laid-open publication (kokai) No. Sho 48-47346
[Patent Reference 4]
Japanese Laid-open publication (kokai) No. 2000-330328
[Patent Reference 5]
Japanese Post-Examination Patent publication (kokoku) No. Hei 1-38043